Preparation And Basic Properties Of Zinc-based Biodegradable Materials

Due to the excellent biocompatibility and moderate degradation rate in vitro,Zn has been widely studied as a new generation of biodegradable materials.However,quite low mechanical properties of pure Zn are not sufficient for bone graft materials.In order to prepare biodegradable materials that meet the mechanical properties of the human body and have a suitable corrosion rate,the method of this article is adding Cu element to improve its mechanical properties and adding HA to improve the biocompatibility of the material.In the present study,a series of Zn-xCu(x=0,1,2,3 wt.%)alloys and Zn-3Cu-xHA(x=0.5,1,2,3 wt.%)composites are fabricated using spark plasma sintering technology(SPS).The relative density,microstructure,hardness,compressive strength and in vitro degradation of the material are investigated.Zn-xCu(x=0,1,2,3.wt%)alloys were prepared by SPS sintering technology.The relative density of the series alloys were all above 95%.Moreover,the intermetallic phase Cu Zn₅ appeared after the addition of Cu.With the content of Cu increased,the relative quantity and grain size of the second phase increased,while the grains of matrix Zn were refined.The hardness and compressive strength of the material gradually increase with the increase of Cu content.When the content of Cu increased to 3wt%,its compressive strength was 2.09 times that of pure zinc,up to 249.32±8.48 MPa.The mechanical properties meet the requirements of human cortical bone(170-193 MPa)demand.The corrosion rate was studied by electrochemical and in vitro immersion experiments.It could be found that the corrosion rate of materials accelerated with Cu content gradually,and the corrosion rate levels of materials measured by electrochemical and immersion experiments were both microns per year.Under this corrosion rate,the mechanical properties can be maintained for 3-6 months after implantation in the human body.The corrosion product was mainly Zn₅CO₃(OH)₆,which was non-toxic and harmless to the human body.The Cu Zn₅ phase corroded slightly,and the morphology after corrosion showed a porous structure.Considering comprehensively,Zn-3Cu alloy with a content of 3 wt.%is most suitable for biodegradable bone graft material.After adding HA,considering that HA is not conductive and does not react with the matrix,it will affect the sintering quality of the material.So we explored the sintering process.We found the formation mechanism of Cu Zn₅ during the sintering process.Zn gradually diffuses from the outer layer of the Cu particles to the inner layer.During the diffusion process,the?phase and the?phase are formed.,Zn diffuses into the Cu particles with the sintering time increased,finally changing to Cu Zn₅ phase which is uniform and single.The density of composite material could reach to 95%by increasing the sintering temperature and prolonging the holding time after adding HA.At the same time,the Cu Zn₅ phase grew up significantly.HA was mainly distributed at the grain boundary of the material,while part of agglomerated HA would lead to form larger particles.The HA and the matrix were combined by mechanical mixing.With the increase of HA content,it had little effect on the hardness of the material,but the compressive strength gradually decreased.When the HA content increased to 3wt%,its compressive strength dropped to 125.36±8.95 MPa about half of Zn-3Cu.However,the compressive strength of 0.5 wt.%and 1 wt.%of HA was 167.47±8.69 MPa and165.11±5.97 MPa respectively,which met the requirements of cortical bone.The degradation rates of the composite material gradually accelerated with the addition of HA,the degradation rate increased from 9.95±1.16?m/year to 40.23±4.56?m/year,and the degradation product of the material was still Zn₅CO₃(OH)₆.To sum up,the Zn-3Cu-1HA composite material prepared by SPS technology has a compressive strength that matches human cortical bone and a suitable degradation rate.It is a biodegradable bone implant material with excellent comprehensive performance and has potential value.